1. Field of the Invention
The present invention relates to housings for power tools and, in particular to housings that accommodate drive sources, such as electric motors, of power tools.
2. Description of the Related Art
In general, in a power tool having an electric motor as a drive source, the output of the motor is amplified (i.e., the rotational speed of the motor is decreased) by engagement of gears (i.e., a gear train) and is thereafter outputted from an output shaft. The gear train is interleaved between the motor and the output shaft and is accommodated within a gear chamber defined generally within a housing. Grease or lubrication oil is sealingly contained within the gear chamber for the purpose of lubrication of the gear train. The housing generally has a structure split into right and left halves along a lengthwise direction (a motor axis direction) taking into account of ease of assembling and performing the maintenance work.
The split housing has a problem that the oil component of the grease may leak from the gear chamber to the outside via a small gap produced between mating surfaces of the housing halves due to a capillary action during a long time use. In order to prevent the grease oil component from leaking to the outside, Japanese Laid-Open Patent Publication No 5-23978 has proposed a technique of sealing between the mating surfaces of the housing halves. According to this technique, a groove is formed in one of the mating surfaces and a rib is formed on the other of the mating surfaces. The groove and the rib are engaged with each other with a resilient seal member interleaved therebetween. Japanese Laid-Open Utility Model Publication No. 5-20879 has proposed another sealing technique, in which an additional wall for preventing the grease from leaking is provided on the outer side of a wall part that defines the gear chamber, so that the grease can be prevented from leaking by a double wall structure.
However, in the case of the sealing technique of Japanese Laid-Open Patent Publication No. 5-23978, the recess and the rib are necessary to be provided at the mating surfaces of the housing halves. In addition, the separate sealing member is necessary to be interleaved between the mating surfaces. Therefore, the cost of dies for molding the housing halves may increase. In addition, the number of parts may increase. As a result, the manufacturing cost of the housing may increase. Also, in the case of the sealing technique of Japanese Laid-Open Utility Model Publication No. 5-20879, the manufacturing cost may increase because it is necessary to provide the additional wall.
Therefore, there has been a need for a housing for a power tool, which can prevent or minimize the leakage of liquid without substantial increase in the manufacturing cost.